1. Field of the Invention
The present invention relates to a page image displaying device for displaying a page image of a document, and an image forming apparatus.
2. Description of the Related Art
Multi-functional Peripherals (MFPs) known as information equipment for business use are provided with a display on which an operating screen (image for operation) is displayed. For printing a document, the MFP displays an image of a page to be printed in a preview mode on a display combined with an operating panel. The preview mode usually displays a page image showing the appearance of an output state of each of pages of the document. When a user performs predetermined operation for switching between pages, the MFP displays page images, in order, of all the pages of the document.
The MFPs and other type of multifunctional information equipment are provided with a touch-sensitive panel functioning as operation entry means. The touch-sensitive panel herein is a touchpad pointing device used in overlapping relation with a display such as a liquid crystal panel. The surface of the touch-sensitive panel functions both as a screen on which an operating screen is displayed and as a touch screen on which a user performs operation.
A project-type capacitive touch-sensitive panel has capabilities to detect multi-touch actions that are two simultaneous finger touches on the touch screen. This type of touch-sensitive panel is used in mobile information equipment, e.g., a smartphone and tablet personal computer that have been widely used in these days. The touch-sensitive panel is capable of detecting not only single-touch actions such as tap and flick but also multi-touch actions such as pinch and rotate. This enables users to give the information equipment a command via a simple action, even if the command involves complicated actions according to the single-touch actions. For example, a set value of a print magnification can be changed through pinch-in and pinch-out gestures made while the information equipment is put in a preview mode (Japanese unexamined patent application publication No. 2012-123066).
A related technology has been proposed for accepting a predetermined multi-touch action as operation for switching between pages to be displayed. An electronic blackboard switches between images on the screen by one page in accordance with the movement direction of the multi-touch position (Japanese unexamined patent application publication No. 2012-168620).
According to the conventional preview mode in an MFP as discussed above, when page images showing the details of the pages are selectively displayed one by one, the entire page image displayed is replaced with a page image of another page in response to page switch operation. Replacing one page image with another involves processing for rasterizing document data and changing the scaling in accordance with the size of display. The time required for the processing depends on data amount of the page image for replacement.
A user possibly focuses attention on only a part of each page to perform the page switch operation. For example, the user sometimes writes, by hand, page numbers onto document sheets before making a copy or facsimile transmission of the document sheets. The user places the document sheets on a document tray and enters a job start command. In response to the command, the MFP reads images from the document sheets. At this time, the user probably checks whether or not the page numbers are written correctly onto all the pages by previewing the images on the screen. In another case, the user probably checks whether or not a portrait for curriculum vitae or a seal affixed on a paper document is clearly printed. In yet another case, the user may check whether or not description in header/footer is correct.
In conventional technologies, when a user focuses attention on only a part of each page, display of a part to which the user pays no attention is unnecessarily updated in accordance with the page switch operation. This delays the page switch because processing unnecessary for the user is executed. Further, the user possibly focuses his/her eyes on change in part to which no attention is necessary, and thereby he/she overlooks a part to which attention should be paid.